MADRID, Spain (Bloomberg) -- Spain completed ground rules for oil and gas drillers to use hydraulic fracturing, or fracing, spurring shale-exploration projects by endorsing the contested technology that they need.

The main oil-exploration law was modified to specifically allow the water-intensive drilling technique in legislation published today that becomes effective tomorrow. In the same law, fracing projects across Spain will now be required to meet environmental-impact rules. That means the use of pressurized water and chemicals to break up rocks to unlock fuel may be scrutinized for potential impacts on aquifers to air quality.

Spain is one of Europe’s most energy-poor nations, importing about 99 percent of its oil and gas needs. While its traditional fields are few with scant output, the advent of finding fossil fuels using fracing technology has sparked interest by drillers from Spain’s Repsol SA to San Leon Energy Plc of Dublin.

“Now, if a regional government prohibits fracking, that would be in conflict with this national law,” Abel La Calle, an environmental lawyer and professor based in Almeria, Spain, said in an interview. “Previously you could only imply that fracking was permissible. Now it’s expressly legitimized.”

The changes give more legal certainty to exploration companies, said an official of one of their industry groups, Shale Gas Espana, who spoke on condition of anonymity as more senior officials weren’t immediately available to comment.

The national government announced months ago that the rule changes were being drawn up.